1. Field of the Invention
The present invention relates generally to a suspension unit and, in particular but not exclusively, to a suspension unit capable of achieving vibration and shock absorption with a small stroke by joining linear characteristics of metallic springs and non-linear characteristics of a magneto-spring to provide linear characteristics under normal conditions of use, and non-linear characteristics as a whole.
2. Description of the Related Art
In recent years, vehicle technologies including automobile technologies have been remarkably developed, and the safety and riding-comfort as well as the maneuverability are desired. Vibration is a great factor that gives rise to various problems such, for example, as fatigue or vision problems and, hence, to enhance the riding-comfort by a reduction of vibration is an important problem from the viewpoint of active-safety. Because of this, a mechanism for reducing vibration which vehicles cause on the human body is needed, and various vibration models have been hitherto proposed and put into practical use.
In general, vibration characteristics depend on the loaded mass and the input. It is considered that the dependence on the loaded mass is closely related to the curvature of load-deflection curves, while the dependence on the input is closely related to the hysteresis of load-deflection characteristics. In suspension systems for automotive vehicles, it is very difficult to adjust parameters such as the spring constant and the like under various conditions: the road surface condition, the stability of control, the impedance condition and the like.
Suspension systems having low damping characteristics exhibit good vibration characteristics in a high-frequency region, but the vibration transmissibility at a resonant point becomes large and, hence, a large impulsive force cannot be absorbed. In contrast, if the damping characteristics are enhanced, the vibration characteristics in the high-frequency region are deteriorated, though the vibration characteristics at the resonant point and the absorbency of the impulsive force are improved. In order to balance the vibration absorption and the shock absorption in a higher level, a stroke is required. However, if the stroke becomes large, the unpleasant feeling increases, and some problems such as a movement of the eyes, a sway of the body, or difficulties in the control of the pedal are encountered in controlling automotive vehicles.
For these reasons, conventional passive vibration models have a limit on their performance. For the optimization under various conditions, the active control is needed which provides ideal vibration characteristics with a small stroke. However, because the active control applies a force to the system via actuators and the like, it is disadvantageously accompanied by energy consumption. Also, the control characteristics depend on the performance of actuators or sensors and, hence, the active control also has a limit on its performance. Furthermore, the active control makes use of electric energy and is, therefore, not entirely satisfactory in reliability.
Recently, with the practical use of permanent magnets that have a high coercive force and a high residual magnetic flux density, research is flourishing in areas such as mechanical structures and magnetic systems that utilize magnetic levitation, magnetic bearings, dampers employing a magnetic fluid, or the like. Because magnetic levitation damping technology makes it possible to support physical objects with no actual physical contact, its merits include reduction of problems related to friction and wear, the capability for motion at very high speeds, and low levels of vibration and noise. Furthermore, it can be used in special situations (also a special characteristic of magnets), as well as having the advantage of its force being effective in all directions For these reasons, magnetic levitation vehicles, magnetic bearings or the like which apply those special characteristics are being developed.
Of the levitation technologies that utilize magnetic forces, the majority utilize attractive forces. Magnetic circuits that make use of repulsive forces are difficult to utilize in vibration control systems, due to their instability and the fact that they are difficult to control (due to the marked non-linear characteristics of the repulsive forces).
The present invention has been developed to overcome the above- described disadvantages.
It is accordingly an objective of the present invention to provide a suspension unit capable of achieving vibration and shock absorption with a small stroke wherein linear characteristics of metallic springs and non-linear characteristics of a magneto-spring are joined to create a xe2x80x9ccombination springxe2x80x9d which has linear characteristics under normal conditions of use, but which is a non-linear spring system as a whole.
In accomplishing the above and other objectives, the suspension unit according to the present invention includes a lower frame, an upper frame vertically movably mounted on the lower frame, and two link mechanisms disposed on respective sides of the upper and lower frames for connecting them to each other. Each of the two link mechanisms includes a parallel link mechanism having two arms extending generally parallel to each other and a pantograph-shaped link mechanism having a plurality of arms. The suspension unit also includes two permanent magnets each fixedly mounted on one of the upper and lower frames with like magnetic poles opposed to each other, a metallic spring engaged with one of the pantograph-shaped link mechanisms, and a shock absorber engaged with the other of the pantograph-shaped link mechanisms that has spring properties.
With this arrangement, vibration below a predetermined amplitude is absorbed by the spring properties of the other of the pantograph-shaped link mechanisms with shock absorber not operated. furthermore, a combination of the linear characteristics of the metallic spring and the non-linear characteristics of the magneto-spring provides non-linear spring characteristics having a linearity in the region of normal use. Such characteristics achieve vibration and shock absorption with a small stroke.
Advantageously, the suspension unit further includes a plurality of metallic springs engaged with the upper frame and with a portion of the parallel link mechanism for producing a lifting force of the upper frame. It is therefore possible to provide a suspension unit having any arbitrary spring characteristics by appropriately setting the spring constant of the magneto-spring and that of the metallic springs.
Preferably, the shock absorber has spring properties in a direction axially thereof. With this construction, fine vibration to which input vibration has been attenuated is absorbed by the non-linear characteristics of the magneto-spring and the link mechanisms without being transmitted to the shock absorber, thus improving the vibration characteristics particularly in a high-frequency region.
Again preferably, the shock absorber has spring properties in a direction in which each end of the shock absorber slides. With this construction, fine vibration to which input vibration has been converted by the link mechanisms is not transmitted to the shock absorber, making it possible to improve the vibration characteristics in high-frequency and low-frequency regions.